1. Field of the Invention
This invention relates to a process for purification of contaminated fluids by disinfection and/or reduction in chemical oxygen demand by means of plasmas generated by focused laser radiation.
2. Description of the Prior Art
The disinfection of water and wastewater by the addition of chlorine, calcium hypochlorite or sodium hypochlorite is widely practiced. Disadvantages of chlorine disinfection include undesirable taste and odor properties of the treated water, and the formation of chlorinated organic compounds which have potentially harmful properties when ingested.
An alternative to chlorine in the disinfection of water is ozone, a strong oxidizing agent which not only destroys microorganisms but also oxidizes many organic compounds to innocuous species, e.g. acids which are similar to those found in natural waters.
The use of ozone in conjunction with ultraviolet light, which combination will oxidize certain organic molecules refractory to ozone alone, has been investigated (H. W. Prengle, Jr. et al., Hydrocarbon Processing, pp. 82-87, October 1975). The combination of ozone and ultraviolet light also destroys certain inorganic contaminants such as cyanide and ammonia.
Laser plasma is generated by focusing Q modulated laser radiation. The plasma, which resembles an electrical spark discharge, is characterized by high temperatures, escaping electrons which give rise to X-rays, ions produced by ionization of the gaseous medium surrounding the plasma and the possibility of neutrons. Laser plasmas have been produced using a variety of lasers, e.g. CO.sub.2 lasers with wavelengths of 9.2-10.6 .mu.m, Nd:YAG-Nd:glass lasers with wavelengths of 1.06 .mu.m, ruby lasers with wavelengths of 0.69 .mu.m at room temperature and iodine lasers with wavelengths of 1.3 .mu.m. The laser plasma is developed by focusing the energy of the laser radiation into extremely small areas, e.g. a 1 Joule CO.sub.2 (10.6 .mu.m, 1-n sec pulse) laser focused to a diameter of approximately 50 .mu.m resultes in a power at the focal point of approximately 5.times.10.sup.13 W/cm.sup.2 [R. P. Godwin, Laser Interaction and Related Plasma Phenomena, Vol. 3B, H. Schwarz and H. Hura (Eds.), Plenum Press, New York, 1974, pp. 691-711].
When laser plasmas are produced in air or oxygen, ionic and charged molecular oxygen species as well as atomic oxygen and ozone are produced in the plasma. Molecular species such as ozone, which are relatively stable in air or oxygen, escape the plasma and remain present in the surrounding gas. Electronic transitions in oxygen and nitrogen atoms and molecules, present in the plasma, produce ultraviolet emissions during subsequent electronic relaxations, particularly in the cooler, outer regions of the plasma.
Recently the effects of unfocused laser radiation on biological systems have been investigated [Pratt, George W., Biomed. Phys. Biomater. Sci. Lect. Summer Program, 1971 (Publ. 1972) 301-20, edited by Stanley, H. Eugene MIT, Cambridge, Mass.]. Unfocused CO.sub.2 and CO lasers, with radiations in the infrared region, were used to deactivate spores or metal surfaces or spores absorbed in paper substrates. In this particular case, sterilization is accomplished, thermally, by rapidly heating the surface of the metal or substrate with incident infrared laser radiation to sufficiently high temperatures, e.g. 500.degree. C., which accomplishes the sterilization procedure. The unfocused laser radiation does not produce a plasma. Therefore, the plasma components, ozone, ultraviolet light, ions, electrons and X-rays are not used to effect sterilization.
More recently, unfocused laser radiation at a wavelength of 1.06 .mu.m has been used to inactivate bacteria, e.g. E. coli [J. G. Parker, Water and Sewage Works, Vol. 123, pp. 52-53, May 1976]. In this particular application, the unfocused laser radiation interacts with dissolved oxygen which is excited to the singlet '.DELTA..sub.g electronic state. The excited singlet oxygen molecules collide with microorganisms resulting in inactivation. Again, the laser radiation that was used was unfocused and the plasma components, ozone, ultraviolet light, ions, electrons and X-rays, were not utilized in sterilization.
Hoskins U.S. Pat. No. 3,405,045 (Oct. 8, 1968) describes a process for irradiating monomer solutions with laser radiation to form free radicals and thereby initiate polymerization.